I was recently given an original Q-Tron by a friend of mine. With all of that empty real estate inside the case I was thinking that it would be great to add a volume control to it that would only be active when the effect is on. That way, I could dime my guitar in order to provide enough juice to open the envelope and yet have the volume level where I need it (clearly, I don't have an OBEL in my guitar).

Has anyone done this before? If so, could you share with me how you did it?

Does the original have a gain? If so that's how set my sensitivity. I toggle between between my homemade stratoblaster pre set at 6db w/no gain knob and waldo's tpc-1. I get a slight cleaner blast with my homemade than the tpc-1. Both are toggled between exact and very short as possible to my pup wires. With the TPC-1 I have to bring my qtron"s gain to about 5 and with and with my homemade perf board jobby around 3-4 just enough so you see the gain led flash on your weakest octave. Without the obel you'll be all over the place the qtron like many others are a volume sensitive pedal. So what you mean is you want to put a blend knob in the circuit so the pedals settings are at full open waoom and you want to go from no effect to blending it in so it takes over your sound like an fx level knob. Tricky question. I just dont see how anyone can play with out an obel when they so easy to design in any guitar. Actually all pedals tone are affected by just having them on the end of your volume knob. Next closest is to use a combo amps fx looop if it has one. Then just built and external loop and tru-bypass it. Have your volume pre set on the guitar and don't touch and use a volume pedal for leads and or make your volume adjustments on your pre/amp

If you're just not willing to modify the guitar for an OBEL , and don't want a volume pedal taking up space, that seems like a great solution to me to put a volume control just before the out jack of the Qtron .